The present invention relates to a discharge lamp device having a cathode made of a semiconductor ceramic material.
There are known discharge lamp devices employing cold cathodes such as a sodium vapor lamp. The cathode or discharge electrode of such a discharge lamp comprises a coiled tungusten filament to be heated that is coated on its surface with an electron-emitting material, which is an oxide mainly composed of barium, strontium, and calcium.
The conventional cathode has however been disadvantageous in that the electron-emitting material tends to evaporate and react with mercury vapor filled in the lamp tube, failing to meet various desired requirements as to heat resistance, chemical resistance, and discharge characteristics of discharge lamp devices. Another problem is that since tungsten is expensive, the cost of the discharge lamp devices is high.